1. Field of the Invention
This invention relates generally to elastic couplings for coupling two rotating mechanical devices. The invention more particularly relates to an elastic coupling comprising: a first coupling member having an outer ring, an inner second coupling member having axial recesses, and a plurality of substantially radially extending leaf spring means having inner and outer ends, said leaf spring means being mounted with their outer ends in said first coupling member and extending with their free inner ends into said axial recesses, each of said leaf spring means comprising a plurality of axially adjacent strips.
2. Description of the Prior Art
A shaft coupling having radial leaf spring means is known, for example, from German Pat. No. 1,202,590. With this prior art arrangement each stack of leaf springs consists of a plurality of superimposed substantially radial leaf springs. Some of the super imposed leaf springs have the same lengths and extend radially inwards into the axially extending recesses of the inner second coupling member. Only on one side of these leaf springs, the stack of leaf springs comprises additional leaf springs of lengths reduced in steps. The stacks of leaf springs are held by intermediate pieces. These intermediate pieces have substantially trapezoidal cross section, which becomes narrow radially inwards. The outer surfaces of the intermediate pieces are cylindrical and are curved about the axis of the outer ring. The outer ring has a conical inner surface, and a slotted ring having a correspondingly conical outer surface is located between the outer ring and the intermediate pieces. When the outer ring and the slotted ring are tensioned towards each other by screw bolts, which tighten the two cover members, the slotted ring will, at the same time, be contracted in peripheral direction, and this will cause also contraction of the intermediate pieces in peripheral direction and clamping of the stacks of leaf springs.
Due to the rings, which have to be quite solid, as they are to perform the clamping function, a considerable proportion of the radial dimensions of the coupling gets lost and cannot be utilized for spring length and thus for increased elasticity of the coupling.
As the shorter leaf springs do not engage the recesses of the inner second coupling member, they become effective with one direction of rotation only in which they are taken along by the bent longer leaf springs while they remain inoperative with the opposite direction of rotation. Thus with the latter direction of rotation this coupling has a different spring characteristic and a smaller transmittable torque than with the former direction of rotation.
Mounting of the leaf spring means is effected by frictional contact with the rings and not by positive engagement.
It is also known to fill the sealed inner cavity of such an elastic shaft coupling with a damping liquid. Chambers are defined by the stacks of leaf springs, and the volumes of these chambers are expanded or reduced by vibrations of the coupling members relative to each other. The damping liquid displaced thereby through the narrow slots between these chambers causes damping of the vibrations (German Pat. No. 1,206,219). Such slots are formed both between the intermediate pieces and the inner second coupling member and between the stacks of leaf springs and the cover members.
With this coupling the stacks of leaf springs comprise central, long leaf springs, which engage the axially extending recesses of the inner second coupling member and, on both sides of these long leaf springs, additional leaf springs of stepwise reduced length.
In order to permit angular offset of the coupling members, the intermediate pieces and the inner coupling member face each other with concave and convex, respectively, spherical surfaces. In the prior art arrangement, radial offset of two shafts to be coupled with each other is permitted by two angularly movable elastic shaft couplings which are combined with an intermediate shaft portion to form a universal-joint shaft.
With the prior art shaft coupling, the two coupling members cannot be radially movable relative to each other, because such radial mobility would require correspondingly wide slots, for example between the intermediate pieces and the inner second coupling member and, correspondingly, would ruin the damping. Also, even a deformation of the leaf springs by twisting in the case of purely angular offset would affect the slot width between the stack of leaf springs and the cover members. It is not possible to adjust the damping in accordance with the individual requirements.
By the symmetric design of the stacks of leaf springs, the same spring characteristic is obtained for both directions of rotation. However, only half of the shorter leaf springs become effective with each of the two directions of rotation.
Furthermore, an elastic coupling of this type with oil damping is known (German Pat. No. 1,222,324) with which sealing ledges are provided between the intermediate pieces and the inner second coupling member in the planes of symmetry of the intermediate pieces. Thereby the inner cavity of the shaft coupling is subdivided into chambers, each of which is in turn subdivided into two partial chambers by the stack of leaf springs. Oil supply passages end on the bottom of the axially extending recesses, which are engaged by the stacks of leaf springs, said passages extending within the inner second coupling member and communicating with a filling pump through a restrictor. In the position of rest of the coupling, oil return passages end in the planes of the sealing ledges guided in the intermediate pieces. With rotation of the coupling members relative to each other in one direction, the stacks of leaf springs bend and engage the surface of the axially extending recesses. Then oil from the filling pump is pumped through the oil supply passages into the chamber formed on the opposite side of the stacks of leaf springs. The chambers on said one side of the stacks of leaf springs are connected to the return passages due to the angular displacement of the sealing ledges. Thereby the leaf springs are supported by the filling pump pressure in a sense counteracting the deflection. With vibration of the coupling members relative to each other, in addition, oil is urged through the slots between the stacks of leaf springs and the cover members as well as the second coupling member, and thus damping of these vibrations is achieved.
With this coupling the static seal between the cover members of the first coupling member and the second coupling member precludes any radial mobility.
With all couplings described, all leaf springs have to be twisted to permit angular displacement. Such twisting is opposed with considerable torque by the leaf springs, such torque loading the bearings of the parts to be coupled. Therefore the angular offset permitted by such prior art shaft couplings is only small as compared to existing requirements.
Couplings have already been provided, in which each leaf spring means consists of two axially adjacent strips of equal width. Such a two-part arrangement is, however, not able to solve the problems mentioned in unobjectionable manner. Each individual strip namely is subjected to twisting, when the coupling members are angularly offset, said twisting resulting in strong curvatures in the axially outer areas of each strip and in a substantially smaller curvature in the axially inner areas of the strip. This strong curvature of the outer area of each strip relative to the inner one integral therewith results in considerable elastic restraint against the twisting, and this is not changed substantially by subdividing the leaf spring means into two strips of equal width.
Another problem is that with such an angular offset the slots formed between the leaf springs and the adjacent parts of the coupling will vary, whereby the damping characteristic of the coupling can vary uncontrollably.